Send to Back may not appear to work for these reasons:
Ø Are too many objects selected? If the object you're sending is selected, but the object you want in front is also selected, the net effect will be no change. Make sure only the object you want sent behind is selected.
Ø Are the objects part of a group? Try ungrouping them and select individual objects to SendToBack.
Ø You can't send behind or bring in front of the grid, but you can change the grid's properties to do that for all objects.